Many chemicals which are biologically inert undergo biotransformation in the body to highly reactive intermediates which attack various cellular macromolecules. Nuclear DNA and the protein, lipid and RNA components of the drug metabolizing enzyme systems (DMES) have been shown to be targets of these reactive metabolites when the parent compound is administered acutely. The progression of biological changes during the adaptation to long-term exposure to injurious and often carcinogenic chemicals in relation to liver DNA metabolism and liver DMES activity will be the subject of this investigation. The administration of CC14 to mice for 32 weeks or or phenobarbital to mice for 52 weeks results in a high incidence of hepatocytic neoplasia. Using these two models of chemical carcinogenesis, liver DNA metabolism and liver DMES activity will be studied at periodic intervals from the start of the experiment through the development of neoplastic tissue. Liver DNA damage will be determined by density gradient sedimentation in alkaline sucrose or alkaline NaI following appropriate labelling of nuclear DNA. Further analyses of liver DNA metabolism will include estimation of repair synthesis, digestion of chromatin by micrococcal nuclease, extraction of DNA subunits followed by their digestion with restriction endonucleases and separation of the fragments by agarose gel electrophoresis. The enzymatic studies will utilize liver DNA labelled in vivo with (3H)dTHr or (3H)dGR and liver DNA extracted following the in vivo administration of 14C-CC14 or 14C-phenobarbital. Complementary experiments will include an estimation of liver DMES activity using both type I and type II substrates. The primary objective of this research program is to test the hypothesis that a CC14 metabolite interacts with liver DNA producing DNA damage and repair synthesis which during the course of chronic CC14 administration involves continuing invasion into DNA covered by chromatin protein, while covalent binding of PB metabolites to DNA at first preferentially involves DNA covered by chromatin protein but progressively includes nuclease accessible DNA.